The proposed investigations represent continuations of ongoing research activity on the field of immunology and the gastrointestinal tract. Particular emphasis has been and will be placed on the production and characterization of specific antibodies to gastrointestinal polypeptide hormones. The antibodies have been and will be utilized for the intracellular and tissue localization of polypeptide hormones as well as measurement of these hormones, for example gastrin in serum and plasma. Specific immunological methods, including fluorescein, labeled antibodies to gastrin and horseradish peroxidase labeling of antibodies to gastrin, have been used and will be used for localization of gastrin in various sites including the stomach, small intestine and pancreas. Other applications in the field of gastroenterology by immunological and immunochemical techniques include studies concerned with the roles of the gastrointestinal tract in the immune response and the function of the sensitized lymphocytes in idiopathic diseases of the gastrointestinal tract. BIBLIOGRAPHIC REFERENCES: Maher, J.W., Wickbom, G., Woodward, E.R., McGuigan, J.E., and Dragstedt, L.R. The effect of vagal stimulation on gastrin release and acid secretion. Surgery 77:255-260, 1975. Wickbom, G., Landor, J.H., Bushkin, F.L., and McGuigan, J.E. Changes in canine gastric acid output and serum gastrin levels following massive small intestinal resection. Gastroenterology 69:448-452, 1975.